Isothermal vapor-liquid equilibrium measurements and PC-SAFT, PR78, and CPA phase behavior modeling of n-tricosane + SC CO2 mixtures

Abstract

This study reports the isothermal VLE (PTxy) data of n-tricosane (heavy n-alkane, n-C23H48) in supercritical (SC) CO2 at two selected temperatures of (323 and 343) K over the pressure range from (1.66 to 34.88) MPa. The measurements were made using a high-temperature and high-pressure VLE optical cell. The combined expanded uncertainty of the temperature, pressure, and phase concentration measurements at 0.95 confidence level with a coverage factor of k = 2 is estimated to be 0.2 K, 0.22 %, and 3.5 %, respectively. The measured VLE data has been used to estimate the critical parameters (TC, PC, xC) of the binary n-tricosane + CO2 mixture. The derived L-G critical properties data of the binary n-tricosane + CO2 mixture are: TC = 323.15 K, PC = 34.02 MPa, xC=0.060 mole fraction of n-tricosane; and TC = 343.15 K, PC = 40.14 MPa, xC=0.071 mole fraction of n-tricosane. The measured solubility data for the mixture has been used to estimate the physical meaning Krichevskii parameter ∂P∂xTCVC∞=-75.93MPa. Based on the derived Krichevskii parameter the thermodynamic (partial molar volumes, V¯2∞,H¯2∞,C¯P2∞) and structural (cluster size,Nexc∞) properties of the infinite dilution mixture of n-tricosane + CO2 near the critical point (CP) of pure solvent (CO2) have been calculated. The measured vapor – liquid equilibrium data for n-tricosane + CO2 was modeled using three equations of state (PC-SAFT, PR78, and CPA). The best prediction option with PC-SAFT was obtained with kij=0.12, while kij=0 was the best using PR78 and CPA EoS.